Last month, Macau, which reverted back to administration of mainland China in 1999 after some 400 years under Portuguese rule, passed a bill that effectively bars Hong Kong residents from visiting the former colony. The ban comes as part of a strict new security law that increases the punishment for treason and subversion against the Chinese government.

Authorities in Hong Kong, a region typically known for outspokenness, have protested what they see as Macau’s attempt to stamp out freedom of speech. Hong Kong, which reverted to China in 1997 after years of British rule, canned a similar law in 2003 amid strong protests over the possible curbing of civil liberties. For its part, Macau appears to be warning Hong Kong to keep out of its affairs.

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“We cannot see why the relationship between the two places, which are meant to be like brothers, could have got so bad,” Albert Ho, chairman of the Hong Kong Democratic Party, told Agence-France Presse.

EU authorities have also voiced concern with the Macau government over the travel ban, wondering if it may affect their own travels to the area, now home to the world’s largest gambling industry.

Beijing currently maintains a policy of “one country, two systems” for Macau and Hong Kong, allowing each region a 50-year period to transition to the economic and political systems of the Chinese government.

Negative international publicity could deal a severe blow to Macau’s burgeoning economy. Heavily reliant on gambling and gaming-based tourism, foreign investment in the former Portuguese territory is now largely geared towards “mega-casinos” rather than smaller establishments.

Macau’s gambling sector dates back to the 19th century, when the Portuguese sought an alternative to the slowing seafaring trade on which the colony had been building its wealth since the 1500s.

First populated by some 50,000 followers of China’s South Sung Dynasty who were fleeing the Mongol invasion in 1277, the Portuguese began to use Macau as a port as early as 1516. China did not officially recognize Portugal’s “perpetual occupation” of Macau until 1887. Nearly a hundred years later, Portugal and China began handover talks, which eventually led to Macau’s reversion to China as a Special Administrative Region on Dec. 20, 1999.